Probabilistic Failure Prediction of High Strength Steel Rocket Motor Cases

In traditional deterministic analysis, uncertainties are either ignored or accounted by applying conservative assumptions. In those cases, only the mean values or nominal values are used in the analysis. Currently, the operating pressure of high strength steel rocket motor cases is predicted by arbitrarily assumed safety factor based on experience. This leads to over weight of motor cases and cost. Hence a methodology is required to predict the operating pressure more accurately by considering optimal safety factor. This paper presents the probabilistic failure assessment methodology to predict the safety factor for the specified reliability using various failure pressure prediction equations. In this study, the scatter in the yield strength, ultimate strength, and thickness of the structure is considered. Monte–Carlo simulation method is used to perform the probabilistic failure assessment. A suitable failure pressure prediction equation is identified among thirteen equations using stress–strength interference theory based on the statistical measure of the predicted and literature test failure pressure. The reliability-based safety factor is computed for the specified reliability with the use of identified failure pressure prediction equation. The safe operating pressure of steel rocket motor cases is computed for the specified reliability levels.